The invention relates to a disc brake for a commercial vehicle having a brake caliper straddling a brake disc. The caliper is mounted so as to be axially displaceable in relation to the brake disc on a stationary brake carrier on two guide bars that are connected to the brake carrier, wherein the guide bars are each guided in a sliding bearing that is non-displaceably held in a bore of the brake caliper.
In the case of such a disc brake, which is also referred to as a “sliding-caliper” disc brake, the brake caliper is connected to a brake carrier on the vehicle side by fastening elements.
To this end, guide bars are connected to the brake carrier for example by screwing, which on the other side are guided in sliding bearings of the brake caliper so that in relation to a brake disc that is non-rotationally held on an axle of the vehicle, an axial displacement of the brake caliper in relation to the brake carrier that is fixed in place is possible.
One of the sliding bearings is designed as fixed bearing with little sliding play and substantially serves for axially guiding the brake caliper, wherein the bearing play is kept as small as possible.
The other sliding bearing, by contrast, forms a loose bearing and, due to its function, has a greater bearing play since, in addition to the axial guidance, tolerance compensation and thermally-induced expansions also have to be taken into account.
As the sliding bearing of the fixed bearing, a metal sleeve is used which, in a manner secured against displacement, is held frictionally engaged in a bore of the brake caliper.
The metal sleeve consists here of a non-ferrous metal, for example brass or bronze, or a composite material, with an outer shell of steel plate and an inner shell, which forms the guiding surface for the guide bar, of a sliding bearing-typical non-ferrous metal, which is connected to the outer shell for example by sintering.
For a lasting operational readiness, a plurality of dimples for receiving lubricants is additionally introduced into the inner surface, i.e. the guiding surface of the sliding bearing.
Altogether, the sliding bearing can only be realized with a substantial expenditure of material and production, with the high costs resulting from this, which are opposed to the constant demands for cost minimization.
The invention is based on the object of further developing a disc brake of the generic type so that it can be more cost-effectively produced with unrestricted functional reliability.
This object is solved by a disc brake for a commercial vehicle having a brake caliper straddling a brake disc. The caliper is mounted so as to be axially displaceable in relation to the brake disc on a stationary brake carrier on two guide bars that are connected to the brake carrier, wherein the guide bars are each guided in a sliding bearing that is non-displaceably held in a bore of the brake caliper. At least one of the sliding bearings is formed of at least two metal sleeves which are arranged spaced from one another in the axial direction and lie against the guide bar, and at least one spacer sleeve positioned between them.
Through the invention, the material proportion of the sliding bearing assuming the guidance in relation to the guide bar is significantly reduced, as a result of which a substantial cost saving materializes since, as described with respect to the prior art, the material provided for the guidance is relatively high in its procurement costs.
The width of the at least two metal sleeves according to the invention is adapted to the displacement path of the brake caliper, even with worn brake pads, in such a manner that even in a position of the brake caliper that is maximally displaced in relation to the guide bar an adequate guidance of the guide bar is ensured.
To this end, with simultaneously optimizing the use of material, the metal sleeve facing the brake carrier is, as provided according to a further aspect of the invention, shorter than the metal sleeve located opposite and defining the end region of the sliding bearing.
The same is dimensioned so that, as mentioned, the brake caliper still ensures an adequate guidance of the brake caliper on the guide bar even in the case of a maximal displacement, i.e. in the case of the complete permissible wear of the brake pad.
The spacer sleeve keeping the distance between the two metal sleeves can be produced from a more cost-effective material than the metal sleeves. An appropriate material is, for example, a plastic with sufficient intrinsic stiffness that compression in the axial direction is not possible.
Since the spacer sleeve exclusively has to fulfill the task of maintaining a distance, no diameter tolerances have to be essentially maintained, wherein the spacer sleeve can also be positioned with play in relation to the guide bar.
Obviously, it is also possible to produce the spacer sleeve from metal instead of a suitable plastic, for example a cost-effective steel plate or as a section of a tube.
In a further development according to the invention, the bore of the brake caliper receiving the sliding bearing is formed as a stepped bore with a smaller diameter on the region facing the brake carrier, wherein this region, in its depth, corresponds approximately to the length of the inserted shorter metal sleeve, which in its outer diameter is matched to the clear diameter of the region of the bore with the smaller diameter so that a press fit materializes.
The metal sleeve located opposite accordingly is so much larger in its outer diameter that sliding into the region with the smaller diameter is prevented.
It is thereby ensured that the sliding bearing during the assembly is always inserted into the bore correctly, i.e. on the correct side, so that a malfunctioning by placing the shorter metal sleeve in the region is excluded, which is to ensure a guidance in relation to the guide bar even in a maximal displacement position of the brake caliper.
The assembly of the sliding bearing as a whole is effected in such a manner that the two metal sleeves and the spacer sleeve positioned between them are placed onto an insertion tool, for example a mandrel, with which the sliding bearing is then inserted into the bore, the shorter metal sleeve upfront.
The shorter metal sleeve in the inserted end position lies against a constriction of the bore which serves as stop for the sliding bearing as a whole, wherein the metal sleeve on its face end facing away from the spacer sleeve comprises a circumferential introduction bevel in the outer shell region, preferentially in the form of a chamfer, so that sliding into the bore with the smaller diameter is possible without problem.
Instead of the mentioned chamfer on the shorter metal sleeve as the insertion aid, the bore with the smaller diameter can obviously also be suitably configured in the region of the stepping.
The invention described in relation to the fixed bearing can obviously be employed also with the other sliding bearing, the loose bearing, if applicable subject to suitably modifying the metal sleeves and/or the spacer sleeve in order to take into account the functions that are different in relation to a fixed bearing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.